This pic shows the different trans cases
and the chassis mount types they accept.

The MK2 chassis uses a bracket that
attaches to the trans using three long 13mm bolts and nuts. The holes are
circled in yellow.

The MK1 chassis uses a bracket that fits
onto the 3 studs around the case edge, in the blue squares.

You can find cases that are MK1 only, MK2
only, and then both, like the one shown in the pic.

The cases that don't have the 3 studs still
have the holes so the studs can be added.... or so I thought. I recently
(5/08) was informed of an ACN14046 trans that has the MK2 holes, but no
studs for the MK1, and no threaded holes to put the studs.